Electron discharge device



July 22, 1958 M. v. mom 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 1956 3 Sheets-Sheet 1 INVENTOR,

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July 22, 1958 I HOOVER 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 195a s Sheets -Sheet 2 25 Q a/H INVENTOR.

4 1; Marie IlHoover j I:

l I I l ATTORNEY "July 22, 1958 M. v. HO0VE R 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 1956 ,I 3 Sheets-Sheet 3 I NVENTOR.

Merle IZHoover ,ywwd W TOR NE 1 .diation from the directly heatedcathodes.

United States Patent ELECTRON DISCHARGE DEVICE Merle V. Hoover,Lancaster, Pa., assignor to Radio Corporation of America, a corporationof Delaware Application March 9, 1956, Serial No. 570,532

14 Claims. (Cl. 313-307) This invention relates to electron dischargedevicesand particularly to improvements in so. called. super-powerdevices capable of an output of the order of half a million watts ormore. This application is a continuation-in-part of my copendingapplication, Serial No. 318,245, filed November 1, 1952.

There are two basic types of super-power tubes. One of these types,the'first type of super-power tube to be developed, comprises acylindrical beam-former having a plurality of longitudinally arrangedslots therein, with an elongated cathode or filament disposed withineach cross bar of each T serves to shield a grid element on each side ofthe vertical portion of the T from the parts of the anode which areradially opposite said grid elements. This type of super-power tube is.described by L. P. Garner in U. S. Patent No. 2,636,142.

One of the factors which limits the performance of the super-powertubes, of both the unshielded and shielded types, is the griddissipation capabilities, bothv electrical and thermal. The grids ofsuper-power tubes, like the grids of low power tubes, are heated bythermal ra- Because of the mechanical, electrical, and electron opticalproblems associated with the proper positioning of the grids insuper-power tubes, the grid supporting structure used provides only aone or two line contact at each end of the elongated grids, affordingonly a limited path for conducting heat from the grids. While this gridsupporting arrangement has proven to' be the most satisfactory oneavailable, it does not represent an ideal arrangement for conductingheat away from the grid elements.

Another problem which has arisen in connection with the. shielded triodeversion of the super power tube is that, because of the arrangement ofthe T-shaped shield, the number of unit triodes which can be placedaround a beam former of given diameter has been reduced from, forexample, forty-eight to twenty-four. This has necessarily reduced thepower output. Increased power output could be obtained by enlarging thediameter of the beam former and consequently the diameter of the anode,but it would also increase the total interelectrode capacitance. Thiswould seriously limit the upper frequency operation of the tube. Sinceone of the principal reasons for making the shielded triode version ofthe tube was to provide a substantial decrease in. grid-plate.capacitance, and thus raise the maximum operating frequency of the tubewithout resorting to grounded grid circuit out- 2,344,752 Patented July22, 1%58 "ice put, achieving more power at the expense of greatergrid-plate capacitance would be undesirable.

In addition, if a tube has a high power output, and especially if thetube has an output of a million watts or more, it is highly desirablethat the amount of power necessary to drive the tube be as smallaspossible. Reducing the required driving power may be achieved byplacing the grid elements closer together to exert a greaterinfluenceupon the flow of electrons between cathode and anode, but inthe past such arrangements have resulted in higher grid currents. I

Also, since super power tubes are relatively expensive, anything whichcan be done to increase the life of the tube would considerably enhanceits desirability so far as the purchaser of the tube is concerned.

A principal object of the present invention is to provide an improvedpower tube capable of large power output and a long useful life.

Another object of the present invention is to provide an improvedelectrode structure for a power tube which will decrease grid powerabsorption in the tube.

A further object of the present invention is to provide an improvedelectrode structure for a power electron tube which more effectivelyshields the grids from direct thermal radiation by the cathode.

Yet another object of the present invention is to provide an electrontube which makes possible greater power output with a beam former havinga given peripheral surface than has been heretofore practicable.'

A still further object of the present invention is'to reduceinterelectrode capacitances in an electron tube.

Still another object of the present invention is to provide an electrontube capable of high power output and in which small excitation powerwill drive the tubeto its full output capabilities.

An ancillary object of the present invention is to provide a shieldedtriode having improved electron-optical characteristics.

Briefly, an electron tube made in accordance with one feature of thepresent invention comprises a beam former electrode which has at leastone undercut recess or channel. in a surface thereof, and a cathodeextending along and within said channel and having a width approximatelyequal to the width of the aperture of said channel. In accordance withanother feature of this invention, a pair of grid elements are mountedadjacent the bea'm former, one on each side of said channel to form aunit triode structure with the tube anode.

In actual practice, however, more than one unit triode is usually used,the beam former electrode being either planar or cylindrical inform, andhaving a plurality of spaced apart undercut channels, with a cathodeextending along and within each of the channelsand grid elementsextending along the sides of the channels.

In providing the beam former with undercut channels rather thanrectangular channels as described in U. S. Patents 2,544,664 and2,636,142, important mechanical and electrical advantages are achieved.

Increased power output in a tube of given beam former diameter may beachieved if undercut channels or slots are used. For example, each of'the channels shown in Garner et al., 2,544,664, may be undercut toaccommodate larger cathode elements. With all other structural featuresunchanged, the use of larger cathode elements will ,result inrnore spacecurrent and, thus, increased power output. Alternatively, and in someways preferably, undercut slots of the same size and accommodating thesame size cathode elements as those shown in Garner et al. may be used,in which case the grid elements on eachside of the channels may be movedcloser together. Accordingly, a larger number of the unit triodes may bespaced about the circumference of the beam former.

The above described structures will enable an increase in power outputover a tube constructed according to Garner et al. of up to 75%.

The use of an undercut channel in a unit triode which is otherwisesubstantially identical to those disclosed in Garner et al., 2,544,664,will also result in a substantial improvement in the amplificationfactor or mu of such unit triode. The reason for such improvement inamplitication factor is not fully understood. However, it is believed tobe due in part to the better shielding of the cathode from the anode bythe undercut channel, and in part to the relatively closer spacing ofthe grid elements from each other made possible by the undercut channel.

The use of an undercut channel in a unit shielded triode of the typedisclosed in Garner, 2,636,142, produces the advantages above describedand in addition results in -a substantial improvement in the ratio ofanode current to grid current. The reason for such improvement in theratio ofanode current to grid current is not fully understood. However,it is believed to be due to a co-operation between the lips orprojection of the undercut channels the transverse portions of theshields to produce improved electron optics resulting in a moreconcentrated beam. Stated in a different way, it is believed that thelips or projections of the under-cut channels and the transverseportions of the shields cooperate to produce fields which maintain abetter defined electron beam, at least adjacent the grid elements.

Referring to the accompanying drawings:

Fig. 1 is an elevation view of a shielded triode electron dischargedevice constructed in accordance with the present invention;

Fig. 2 is an enlarged partial axial sectional view of the device in Fig.1;

Fig. 3 is a transverse fragmentary sectional view of a portion of theactive electron region of an unshielded triode device constructed inaccordance with the teaching of U. S. Patent 2,544,664;

Figs. 4 and 5 are transverse fragmentary sectional views of the activeelectron regions of unshielded triode devices constructed in accordancewith this invention;

Fig. 6 is an enlarged transverse fragmentary sectional view of theshielded triode device of Figs. 1 and 2 taken along line 66 of Fig. 2;

Fig. 7 is a transverse fragmentary sectional view similar to Fig. 6, butshowing a different embodiment of the present invention; and

Figs. 8 and 9 are transverse fragmentary sectional views similar toFigs. 4 through 7 but showing the present invention incorporated intetrode type tubes.

For the purpose of illustration, the present invention will beprincipally described in connection with shieldedand unshielded triodetypes of super power electron discharge devices. However, it should beunderstood that it is not limited to the particular devices shown. Aswill be apparent, certain features of the illustrated device and themodifications thereof are described and claimed in U. S. Patent Nos.2,544,664, or 2,636,142. Constructional features which are common tosaid patents will not be described in detail here in the interest ofbrevity and clarity except Where necessary for a complete understandingof the present invention.

Referring now to the drawings and to Figures 1 and 2 in particular, anelectron discharge device 20 is shown which is an internally watercooled, super-power, beam triode having a demountable evacuated envelopeas shown.

A plurality of elongated cathode elements 21 constitute a source ofelectrons. Each cathode element 21 is supported adjacent its upper endby a flexible support means indicated generally at 22 which, in turn, issupported from a central supporting conductor 23. The supportingconductor 23 is electrically connected to a terminal ring 24.

The lower or other end of each cathode element 21 is mounted in a ring25 which is brazed to a supporting conductor 26. The supportingconductor 26 surrounds and is coaxial and concentric with the supportingconductor 23. The supporting conductor 26 is connected to a terminalring 27 and below the ring forms part of the exterior or envelope of thetube. A beam former portion 26a (Fig. 6) is provided on the conductor 26above the ring 25 by a plurality of spaced apart channels, slots orrecesses '28, one of the cathode elements 21 being disposed along andwithin each of the slots 28.

A partition 29 extending between the supporting conductors 23 and 26forms two cooling channels for a fluid coolant such as water.

It should be noted that the supporting conductors 23 and 26 are rigidlyconnected by a mechanically strong and hermetic seal adjacent theirupper or inner ends as indicated generally at 30.

Insulated from and supported on the supporting conductor 23 is ahat-shaped support member 31 having a peripheral flange at its lowerextremity with slots and centering or locating if-notches formedtherein. There is one slot for each of a plurality of elongated controlelectrode or grid elements 32. The grid elements 32 each hook into theslots in the support member 31 and are accurately positioned by means ofthe V-notches. Adjacent their lower ends each of the grid elements 32 ishooked into a separate flexible support means 33 which, in turn, issupported from a grid terminal ring 34. The flexible support means '22and 33 are laminated as described in detail and claimed in U. S. Patent2,570,120, issued to W. E. Harbaugh, and assigned to the same assigneeas the instant case. The support 22 is highly flexible while thesupports 33 are each both flexible and resilient.

As is apparent from Figures 1 and 2, an output or anode electrode 35 isprovided which is reentrant and coaxial with the cathode and gridelectrodes. The anode 35 has a plurality of coolant channels 36 formedtherein closed along one side thereof by a loosely fitting sleevelikepartition 37. The inner or upper end'of the anode 35 is closed 'by awall 38 while the other end of the anode vice of U. S. Patent No.2,544,664. Figure 3 is a fragmentary sectional view of a portion of theelectron active region of a tube constructed in accordance with U. S.Patent 2,544,664, having rectangular slots or recesses 41 in the beamformer 26b.

One way of increasing the power output capabilities of the unshieldedtriode tube represented by Fig. 3 is shown in Fig. 4. The width of theopening or aperture 42 of the slots or recesses and the location of thegrid elements 32 with respect thereto are unchanged, but the slots orrecesses 28' are undercut so that the inner portion 43 of the slots 28is substantially wider than the aperture or throat 42 thereof. The widerinner portion 43 of slots 28' permits wider cathode elements 21' to beused without necessitating an increase in the diameter of beam former26b. The increased cathode area results in greater space current beingproduced in the electron stream between cathode elements 21 and anode35. The throat portion 42 of the slots 28 seems to constrict theelectron stream from the wider cathode elements 21' into a moreconcentrated stream than the electron stream in tubes where the slots 41are not undercut. Thus greater power output is possible because of ,theincreased space current from the wider cathode elements 21 and yet thegrid current does not rise with the increased space current as would beexpected.

Conversely, if long useful tube life is more important than increasedpower output, the larger cathode elements 21' may be run at a loweroperating temperature which will extend the life of the cathodeelements.

Fig. 5 illustrates the use of undercut beam former slots 28 with thesame width cathode elements 21 as previously used in super power tubesconstructed in accordance with U. S. Patent 2,544,664 not havingundercut beam former slots and shown in Fig. 3. The arrangement of Fig.5 is more compact than that of Fig. 3 because although the inner part 43of the slots 28 have the same width as the non-undercut slot 41, thewidth of the aperture 42 is less, which permits the grid elements 32 tobe more closely spaced and thus allows more unit triodes to be disposedwithin a given peripheral portion of the beam former 2611. Increasingthe number of unit triodes will, of course, increase the power outputcapabilities of a given tube and is often preferable to increasing thevpower output by increasing the width of the cathode elements 21 as isthe case in Fig. 4 because the space current in the cathode-anode regionmay become great enough, in the arrangement of Fig. 4, that the existinggrid structure will not efficiently control the flow of electronsbetween cathode and anode.

emission of the portions of the cathode filament which are overhung willbe inhibited. If the amount of undercutting is reduced, less than theoptimum results will be obtained.

Since super-power tubes of the types described herein consist of aplurality of unit discharge devices contained within a common envelope,developmental experiments are customarily conducted by fabricating atubeconsisting of a single one of the unit devices and subjecting it toexperimental tests. The results of such tests may then be extrapolatedto give performance data for a tube consisting of a given number of unitdevices. For example, a tube fabricated for experiment and test maycomprise an elongated bar of copper having a slot or channel cut.longitudinally along one surface thereof to act as a beam former. Anelongated cathode filament may be suspended within and along suchchannel by appropriate mounting and electrical terminal means. Twoelongated grid elements may be suspended, one along each side of thechannel, by appropriate mounting and electrical terminal means. Amassive anode member may be mounted opposite the opening of the channeland the entire array may be enclosed in a gas-tight container which maybe evacuated and sealed or continuously pumped.

In an unshielded-triode' unit tube constructed according to thisinvention for the purpose of experiment and test, a beam former barhaving an electronically active length of 8 inches and being 0.50 inchsquare was provided with an undercut channel having a depth of 0.10inch. The width of the throat or aperture of the channel was 0.058 inch.The threat surfaces of the channel tapered at an angle of approximately45 downwardly with respect to the surface of the beam former bar until achannel width of 0.10 inch was reached, the remainder of the channelbeing rectangular. A cathode filament having an electronically activelength of 8 inches, a width of 0.057 inch and a thickness of 0.023 inchwas suspended within and along the channel at a depth of 0.0l7inch. Twoelongated grid rods of trapezoidal cross section were arranged one alongeach side of the channel with their broad dimension facing and parallelto the beam former. The grid rods were 0.062 inch thick with a broaddimension of 0.122 inch and a narrow dimension of 0.065 inch and had anelectronically active length of 8 inches. A massive anode electrodehaving an electronically active length of 8 inches and a widthsubstantially larger than the width of the channel was positionedopposite the channel. were spaced approximately 0.034 inch from the beamformer and approximately 0.061 inch from each other, and the anode wasspaced approximately 0.322 inch from the beam former.

By way of comparison, a unit electron tube constructed according to theteaching of U. S. Patent 2,544,664, utilized a rectangular channel 0.10inch wide and 0.10 inch deep in place of the undercut channel of thisinvention. All other physical dimensions were substantially the same asin the unit tube above described. The cathode filament was set to adepth of 0.025 inch in the channel; the grid rods were spaced 0.037 inchfrom the beam former and 0.103 inch from each other; and the anode wasspaced 0.325 inch from the beam former. By comparing the spacing of thegrid rods from each other in each of the above described unit tubes, itwill be seen that the grid rods of a unit tube constructed according tothe teaching of this invention are 0.041 inch closer together.

With a heating voltage of 6.0 volts and a heating current of 48 amperesapplied to the filament of the above unit tube, a cathode voltage ofzero volts, and the anode and grid elements electrically connectedtogether and raised to a potential of 1500 volts, it was found that theunit tube constructed according to the teaching of this inventionproduced an anode current of 7.3 amperes and a grid current of 0.40ampere. By contrast, the unit tube constructed according to the teachingof U. S. Patent 2,544,664 produced an anode current of 6.50 amperes anda grid current of 0.37 ampere. Thus, it will be seen by comparison thata unit tube constructed according to this invention will produce asgreat or even greater anode current with substantially the same gridcurrent and for a smaller transverse space consumed than a unit tubeconstructed according to U. S. Patent 2,544,664. Extrapolation of theabove results to provide operational data for electron tubes of givenbeam former circumference has revealed that an improvement in poweroutput of 38% is possible through the use of the subject invention.

In addition to the power output advantage of the subiect invention, ithas been found that the amplification factor (or mu) will be more thandoubled. For example, in the above described unit tube, constructedaccording to this invention, the amplification factor at the 0.1 amperepoint was 112, Whereas the amplification factor of the unit tubeconstructed according to U. S. Patent 2,544,664, was 44.8. Theexplanation of such improvement is not fully understood. However, twofeatures of the subject invention would necessarily have a directrelation thereto. Since the amplification factor or rnu of a tubeutilizing electron optics, as in the case of super-power tubes, may beconsidered to be a measure of the degree of shielding between the anodeand the cathode, it may be postulated that the undercut channels providebetter shielding of the cathode from the anode, thus increasing the mu.Furthermore, since the spacing between the grid rods may be reduced,according to this invention, it may be postulated that the grid wouldhave greater control over the electron stream, which also would increasethe amplification factor or mu. Regardless of the explanation of theimprovement in the amplification factor, it seems apparent that theundercut channels operate in a substantially different manner fromnon-undercut channels, at least insofar as electron optics areconcerned.

Referring to Figures 1, 2, and 6, the electron tube shown is in fact ashielded triode type of superpower tube such as is described in U. S.Patent 2,636,142. The shielded triode differs from the unshieldedtriode, shown in Figures 3-5 and hereinabove described, in that aplural- The grid rods ity of shield members 44 are provided which areattached directly to the beam former and which extend between the gridrods and the anode. Referring to Figure 6, which is a cross sectionalview of a portion of the shielded triode tube shown in Figures 1 and 2,it will be seen that the shields 44 may be formed by T-shaped membersprotruding from the beam former 26a, the transverse portions or crossbars 44a of which extend parallel to the beam former surface and theanode surface and between the anode 35 and the grid elements 32.

The cross bar portion 44a of the shields 44 may be provided with axialextensions or tabs 44a, as shown in Figure 2, which are electricallyconnected to a cathode terminal ring 45 positioned between the anodeterminal ring 40 and the grid terminal ring 34. Because of thisintermediate positioning of the cathode terminal ring 45, completeshielding between the input and output circuits may be obtained outsidethe tube 20 in addition to the electrostatic shielding provided betweenthe grid elements 32 and anode 35 by the shields 44 within the tube 20.

Although shielded triodes have certain electric advantages overunshielded triodes, the power output of a shielded triode is necessarilyless thah the power output of an unshielded triode of comparable size.The decrease in power output results from the fact that each shield 44takes the place of at least one unit discharge device thus reducing thetotal number of unit discharge devices which may be positioned about abeam former 26a of given circumference.

The use of the undercut beam former channels 28 and 28' with theshielded triode type of super-power tube 20 makes possible an increasein power output of the same magnitude and for the same reason asdescribed above with respect to unshielded types of super-power tubes.Similarly, the improvement in amplification factor or mu also resultsfrom the use of undercut channels 28 and 28' with the shielded type ofsuper-power tubes as with the unshielded types. However, an additionaladvantage in the form of a substantial improvement in the ratio of platecurrent to grid current results from the use of undercut channels 28 and28' in a shielded triode. The explanation of such improvement is notfully understood but seems to result from the co-operation of the edgesof the undercut channels 28 and 28 and the edges of the cross bars 44::of the shield members 44 to produce electron optics which are conduciveto the high ratio of plate current to grid current.

The best results were obtained through the use of undercut channels witha shielded type tube of the construction shown in Figure 7. It will benoted that the structure shown in Figure 7 includes features in additionto the undercut channel 28 which are diflFerent from the prior art. Forexample, the grid elements 32 are square as compared to the trapezoidalgrid elements 32 heretofore used. Other modifications of similar natureare used to conserve space; and thus, the structure shown in Figure 7has been called the fine grain structure. For this reason, directcomparison of the structure shown in Figure 7 to prior art structure interms of the effect of the various features embodied therein on theoperation thereof is diflicult. However, a unit tube constructed for thepurpose of experiment and test having a structure similar to that shownin Figure 7 produced a maximum current division ratio of anode currentto grid current of about 275 as compared to a maximum of about 85 forshieldedtriode unit tubes constructed according to U. S. Patent2,636,142.

In a unit triode having a structure similar to that shown in Figure 7,the beam former channel 28 was 0.100 inch deep and had an aperture 0.058inch wide. The inner portion of the channel was 0.100 inch wide and thethroat surfaces were inclined approximately 45 with respect to thesurface of the beam former. The cathode element 21" was 0.057 inch wideand 0.023 inch thick and was set to a depth of 0.017 inch in thechannel. The grid 8 elements 32 were 0.038 inch square and were spaced0.0625 inch from each other and 0.030 inch from the beam former. Theshield members 44 were spaced 0.110 inch from each other and 0.028 inchfrom the grid elements and had 0.030 inch thick transverse portions 44a.And the anode 35 was spaced 0.322 inch from the beam former. With afilament heating voltage of 6 volts and a current of 48 amperes, acathode voltage of 0 or ground, and the anode and grid electricallyconnected together and raised to 1500 volts, a grid current of 0.020ampere and an anode current of 5.50 amperes were measured.

Undercut beam former slots 28 and 28' may also be used to good advantagein tetrodes. Fig. 8 illustrates a tetrode arrangement in which bothcontrol grid elements 32 and screen grid elements 46 are shieled fromthe anode by the shield member 44.

In Fig. 9 there is illustrated a shielded tetrode in which a double Tshielding member 47 having two transverse portions 47a and 47b is used,the second of the transverse portions 47b extending between the screengrid elements 46 and control grid elements 32.

However, if it is desired to provide some other degree of decouplingbetweenthe control grid elements 32 and screen grid elements 46 withoutafiecting the electron optics of the tube, the second transverse portionor arm 47b of the shield member 47 may extend between the two gridelements for a distance less than indicated in the drawing. The exactlength of the decoupling arms 4711 would have to be determinedempirically.

()ne of the advantageous features of the shielded tetrode of Figs. 8 and9 is the fact that the output circuit displacement currents will notflow on the screen elements 46 and give rise to screen coupled circuitinstabilities of various types. The double T shielding member 47 of Fig.9 further reduces the anode to control grid interelectrode capacitance,which is one of the prerequisites for stable grounded cathode operationat the higher frequencies. In addition, because of the nearness of thescreen grid elements 46 to the shield member 47 and especially to theshield member 47a in the electrode configuration of Fig. 8, the screengrid is continuously bypassed. The shield members 47a and 47b are alsoof value in absorbing and conducting away heat radiated from the hotscreen grid elements 46.

One additional advantage of the use of the undercut beam former is thatit shields the grid elements from the corners of the cathode elements21. While it cannot be stated positively that high grid current is dueto emission beamed from the corners of the cathode elements 21,examination of tubes drawing excessive grid current has shown thatusually some of the cathode elements have had damaged corners whichresulted either from arcing within the tube during operation or fromchipping during manufacture of the filamentary cathode elements of thetube.

From the foregoing it is apparent that electron discharge devicesconstructed in accordance with the present invention are capable ofoperation with greater efficiency at higher power output than devicesheretofore used.

What is claimed is:

1. An electron tube comprising an anode, a beam former spaced from saidanode and having an elongated recessed portion, said recessed portionhaving a throat substantially narrower than the inner part thereof, andan elongated cathode extending along and within the inner part of saidrecessed portion, the width of said cathode being approximately equal tothe width of said throat. I

'2. An electron tube comprising an anode, a beam former spaced from saidanode and having a plurality of spaced apart elongated recessedportions, each of said recessed portions having a throat substantiallynarrower than the inner part thereof, and a cathode comprising anelongated cathode element disposed along and within 't heinner part ofeach of said recessed'portions, the width of each: of said elementsbeing approximately equal to the width. of each of said throats.

3.- An electron tube comprising a beam former havingan elongated recess,said recess having a throat substantially narrower than the inner partthereof, an elongated cathode element extending along and within theinner part of said recess, the width of said cathode element beingapproximately equal to the width of said throat; a grid and an anodespaced from said beam former, said grid comprising an elongated elementextending along each side of the throat of said recess and between saidbeam former and said anode.

4. An electron tube comprising an anode, a beam former spaced from saidanode and having a plurality of spaced apart elongated recesses therein,each of said recesses having a throat substantially narrower than theinner portion thereof, a cathode comprising an elongated elementdisposed along and within the inner part of each recess, the width ofsaid cathode elements being approximately equal to the width of saidthroats, and a grid comprising an elongated element extending along eachside of the throat of each of said recesses and between said anode andsaid beam former.

5. An electron tube comprising an anode, a beam former spaced from saidanode and having an elongated recess, said recess having a throatsubstantially narrower than the inner part thereof, an elongated cathodeelement extending within and along said inner part of said recess, thewidth of said cathode element being approximately equal to the width ofsaid throat, a grid comprising an elongated element extending along eachside of said throat of said recess between said beam former and saidanode, and a shield electrode comprising an elongated element extendingalong each of said grid elements between said grid elements and saidanode and closely electrically coupled to said beam former.

6. An electron tube comprising an anode, a beam former spaced from saidanode and having a plurality of elongated recesses therein, each of saidrecesses having a throat substantially narrower than the inner portionthereof, a cathode comprising an elongated element disposed along andwithin the inner part of each recess, the width of said cathode elementsbeing approximately equal to the width of said throats, a gridcomprising 'an elongated element extending along each side of each ofsaid recesses and between said beam former and said anode, and a shieldelectrode comprising an elongated element extending along each of saidgrid elements between said grid elements and said anode and closelyelectrically coupled to said beam former.

7. In an electron discharge device, a cathode comprising a circulararray of discrete and separate elements, and a generally cylindricalbeam forming member having a plurality of undercut channels in itssurface, each of said cathode elements extending within and along one ofsaid channels, the width of said cathode elements being approximatelyequal to the width of the aperture of said channels.

8. An electron discharge device comprising concentric and coaxiallyarranged cathode, beam former, grid and anode structures formingcylindrical arrays, said cathode and said grid structures each includinga plurality of spaced elements, said beam former having a pluralityv ofspaced elongated undercut beam forming recesses, each of said gridelements extending along one side of one of said recesses, each of saidcathode elements extending through one of said recesses, the width ofsaid cathode elements being approximately equal to the width of theapertures of said recesses, the diameter of said beam former beingintermediate that of said cathode array and that of said grid array, andthe diameter of said grid array being intermediate that of said beamformer and that of said anode.

9. An electron tube comprising a cathode, a beam a. surface thereof,said cathode extending through said channel, one of said grid elementsbeing onv each side of said. channel, the width of said cathodebeingapproximately equal to the width of said channel. at the surface of saidbeam former and approximately equal to the distance between said gridelements, said. anode being spaced from said grid'elements. I

10. An electron tube comprising an electrode having a plurality oflongitudinal undercut slots. in a surface thereof and a pluralityofelongated members of substantially T-shaped cross section extending fromsaid surface, the transverse portions of said elongated members beingremote from said electrode, there being one of said elongated membersbetween each pair of said slots, an array of cathode elements, each ofsaid cathode elements extending along and within one of said slots, thewidth of said cathode elements being approximately equal to the width ofthe aperture of said slots,- and a first and a second array of gridelements, said grid arrays being positioned between said electrode andthe transverse portion of said elongated member, the elements of each ofsaid grid arrays being substantially in register one with another, agrid element of each of said grid arrays being located on each side ofeach of said slots, the spacing between transverse portions of adjacentelongated members being at least as great as the width of the slot whichlies therebetween.

11. An electron tube comprising a cylindrical beam former having aplurality of longitudinal undercut slots in the outer surface thereofand a circular array of elongated metallic members of, substantiallyT-shaped cross section extending from said outer surface, the

transverse portion of said members being remote from mediate that ofsaid beam former and that of said array of said metallic members ofT-shaped cross section at the transverse portions thereof, one of saidgrid elements being located on each side of each of said slots andadjacent to the surface of said beam former, and a hollow cylindricalanode surrounding and spaced from said array of T-shaped members.

12. An electron tube comprising an electrode having a plurality ofundercut .slots in a surface thereof and a plurality of elongatedmembers extending from said surface, there being one of said elongatedmembers between each pair of said slots, a cathode element disposedalong and within each of said slots, the width of said cathode elementsbeing approximately equal to the width of the apertures at said slots,first and second arrays of grid elements, a grid element of each of saidarrays being located adjacent to each side of each of said elongatedmembers, and an anode spaced from said grid elements, each of saidelongated members having a pair of crossbar portions, one crossbar ofeach elongated member extending between the elements of said first andsecond grid array which are adjacent thereto, and the other crossbar ofeach of said elongated members extending between said anode and theelements of the grid array which lies adjacent thereto, the spacingbetween crossbars of adjacent elongated members being at least as greatas the width of the-slot between said adjacent elongated members.

13. An electron tube comprising a hollow cylindrical beam former havinga plurality of spaced apart undercut longitudinal channels in the outersurface thereof, a circular array of cathode elements, each of saidcathode elements extending along and within one of said channelsythewidth of said cathode elements being approximately'equal to the width ofthe apertures of said channels, a circulararray of grid elements,said'array of grid elements being of larger diameter than said beamformer, a grid element being positioned adjacent to each side of each ofsaid channels, and an anode surrounding and spaced from said gridelements.

14. An electron tube comprising a beam former having a plurality ofspaced apart undercut channels therein, an elongated cathode elementextending along and within each of said channels, an elongated gridelement extending along each side of each of said channels, and

an anode spaced from said grid elements, the width of each cathodeelement being approximately equal to the width of each of said channelsat the surface of said beam former and approximately equal to thespacing between the grid elements at each side of said channels. r

' "References Cited in the file of this patent UNITED STATES PATENTSGarner'et a1 Mar. 13, 1951 2,636,141 Parker Apr. 21, 1953 2,636,142

Garner Apr. 21, 1953

